Sexually Transmitted Diseases in the United States: New Trends in a Continuing Epidemic

Sexually transmitted diseases (STDs) remain a significant public health problem in the United States. Despite the progress made in prevention, diagnosis, and treatment of these diseases, the United States continues to have the highest rates of STDs among industrialized nations.¹ National surveillance data submitted to the Centers for Disease Control and Prevention (CDC) in 2007 indicate that reportable STDs -- particularly chlamydia, gonorrhea, and syphilis -- are once again increasing.² Chlamydia cases alone reached a record high of more than 1 million nationwide. This is a startling statistic, but estimates suggest that the annual number of new cases of chlamydia is actually nearly three times greater. Although reported gonorrhea cases rose to 358,366, far fewer than chlamydia cases, they indicate a 5.5% increase over the past 2 years. The increase in gonorrhea was concentrated largely in the South, with a 12.3% rise within the last 4 years, and in the West, with a 31.8% rise during the same period. As with chlamydia, estimates suggest that national gonorrhea cases are also greater, being twice as high as those reported. And even with concerted national eradiation efforts,³ syphilis cases rose to 9,756, with the greatest increase (54%) occurring among men over the past 5 years.

The reasons why the total number of people infected with an STD each year in the United States is substantially greater than the combined surveillance data show are many. Not all cases of reportable STDs are communicated to the CDC4-6 and not all persons at risk are screened for these diseases.⁷ Failing to screen persons diagnosed with an STD for reinfection with the same or a new STD is also a factor,^8-10 as is not testing for STDs at all anatomic transmission sites.¹¹ Accurately measuring the extent of the STD epidemic is further hampered by the fact that other STDs, such as herpes simplex virus (types 1 and 2) and human papillomavirus (HPV), are not included in the national infectious disease surveillance system and that data on them are gathered through health and nutrition surveys of the general United States population.¹² This is the case, even though estimates indicate that the annual incidence of herpes simplex is more than 1.6 million¹² and that there are approximately 5.5 million new cases of HPV infection each year.¹³ Asymptomatic, and therefore undiagnosed and untreated, infections may also contribute to the incompleteness of the STD national profile.¹⁴

The most recent increase in STDs is occurring primarily among teenagers, young adults, and men who have sex with men (MSM) -- groups that are already at greater risk for HIV infection.² These other STDs, particularly those that cause genital ulcers, increase the risk of transmitting or acquiring HIV infection, making their prevention equally important as cofactors.^15,16 All STDs have health consequences¹⁷ -- some of which are long-term and even irreversible -- and the morbidity associated with STDs can be greater in HIV-infected persons and can complicate HIV treatment.¹⁸ Surprisingly, many HIV-infected persons in the United States -- who now number 1.2 million with and without AIDS^19,20 -- are not consistently screened for other STDs.⁴ This is the case, even though the CDC recommends routine screening and early detection and treatment of coinfections^15,21 and even though such screening could reduce HIV transmission by an estimated 27%.²² In an HIV clinic that adopted routine screening for and treatment of other STDs, for example, at least 9 new HIV infections were prevented among the sexual partners of the HIV-infected patients.²³

The most common STDs in the United States are chlamydia (Chlamydia trachomatis), gonorrhea (Neisseria gonorrhoeae), syphilis (Treponema pallidum), human papillomavirus, herpes simplex virus, hepatitis B virus, chancroid (Haemophilus ducreyi), trichomoniasis (Trichomonas vaginalis), and HIV.² Since the national HIV epidemic began, coinfections with other common STDs have been documented in HIV-infected persons. Nevertheless, the numbers of HIV-infected persons who have coexisting STDs, or acquired them subsequent to an HIV diagnosis, are hard to measure. Prevalence data are sketchy at best, having been gleaned primarily from cohort studies that focus on a particular subgroup of HIV-infected persons or on the resurgence of a particular STD in a single locale.^24-29 Studies of genital ulcers^30,31 and population-based studies of incident STDs among HIV-infected persons^32-34 have also been of limited value because they are restricted to a particular time period and place. Attempts to model the transmission dynamics of coexisting STDs, such as chlamydia and HIV, have underscored the complexity of the prevalence-assessment problem.³⁵

Despite these assessment difficulties, worrisome trends with regard to HIV infection have emerged in conjunction with the new rise in incident cases nationwide.¹⁹ These trends suggest that some HIV-infected persons are not consistently engaging in safe sexual practices, even after receiving an HIV diagnosis. Whereas many individuals substantially reduce their high-risk sexual behavior after receiving an HIV diagnosis,³⁶ some HIV-diagnosed persons are contracting other STDs,^34,37,38 and others are knowingly engaging in unprotected sexual relations with partners they believe to have the same HIV serotype.^39,40 For example, a study conducted among 62,264 HIV-infected persons in New York City in 2001-2002 found that 1,466 (2.4%) were diagnosed during the study period with an incident STD -- 626 with gonorrhea, 465 with syphilis, 298 with chlamydia, and 77 with more than one STD -- indicating a prevalence of 4.1%.³⁴ Smaller studies conducted prospectively in Birmingham³⁷ (n = 338) and retrospectively in Baltimore³⁸ (n = 1,150) found the prevalence of incident STDs to be 6.0% and of 13.3%, respectively.

An important factor in the increase in incident HIV infections is unintentional exposure to HIV. Unintentional exposure is possible when the interval between screenings for HIV is greatly protracted (i.e., > 1 year). For example, in a cross-sectional observational study conducted in 6 United States cities, 1,701 MSM, aged 23?29 years, altogether reported engaging in sexual relations with 11,793 new partners.⁴¹ Among the study subjects, 1,075 (63%) disclosed being HIV-negative to 4,253 (36%) new partners before initiating sexual relations. Among the subjects who disclosed their HIV serostatus, 462 (43%) had last tested HIV-negative less than 6 months before participating in the study, 261 (24%) had last tested between 6 and 12 months before, and 352 (33%) had last tested more than 1 year before. Another 80 (7%) subjects tested HIV-positive during the course of the study and possibly exposed 296 of their new partners to HIV infection.

A factor contributing to incident HIV infections among heterosexual women is unawareness of the high-risk behaviors of their sexual partners, such as having unprotected sex with multiple partners, having sex with men, and injecting illicit drugs. The results of a study of 8,295 HIV-infected people (5,156 men and 3,139 women) speaks to the consequences of that unawareness.⁴² Specifically, 34% of black MSM, 26% of Hispanic MSM, and 13% of white MSM admitted to having had sex with women. That only 14% of white women, 6% of black women, and 6% of Hispanic women in the study admitted to having sex with a bisexual man suggests that many women in the study may not have known whether or not their partners were bisexual and, therefore, high-risk. When women are unaware of the high-risk behaviors of their partners, they are likely to be overlooked as being at-risk for HIV infection, even when they are diagnosed with another STD. Moreover, estimates indicate that individuals who are unaware of their HIV-positive status are 3.5 times more likely to transmit HIV to their sexual partners.⁴³

Much needs to be done to thwart the hidden epidemic of STDs in the United States. A proposed global solution is to integrate the national prevention programs for HIV, other STDs, and viral hepatitis^44,45 and to improve HIV surveillance.^46,47 In addition to these efforts, clinical studies are identifying opportunities at the local level. These studies have explored the screening of clients at an urban STD clinic for chronic hepatitis A and B infections,⁴⁸ the vaccination of MSM for hepatitis A and B while receiving STD services,⁴⁹ and the integration of STD screening and vaccination services into a drug rehabilitation program.⁵⁰ Although such studies are important and innovative first steps, additional inroads are needed to resolve what continues to be an intractable public health problem.

Pamela Paradis Metoyer is a medical editor and research associate at Baylor College of Medicine and is the author of numerous articles on health issues.

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